1. Field of the Invention
The present invention relates to a nonaqueous electrolyte battery comprising a cathode, an anode and a nonaqueous electrolyte. More particularly, the present invention relates to a nonaqueous electrolyte battery having a good cyclic characteristic under any environment of low temperature, ambient temperature and high temperature.
2. Description of Prior Art
Lately, there have been developed and supplied various kinds of portable electronic devices such as a video camera with video tape recorder, portable telephones, lap top computers, or the like and it has been necessary to decrease the sizes and weight thereof. Then, a study and development for improving the energy densities of a portable power supplies of these electronic devices such as batteries, especially, secondary batteries have been advanced. Since a lithium-ion secondary battery among them can achieve energy density larger than those of a lead battery and nickel cadmium battery which are conventional aqueous electrolyte batteries, it has been greatly anticipated.
As cathode active materials used for the lithium-ion battery, lithium-cobalt composite oxides, lithium-manganese composite oxides, and lithium-nickel composite oxides have been put to practical use. While they have respectively advantages and disadvantages, the lithium-cobalt composite oxides have a most desirable balance from the viewpoints of capacity, cost and thermal stability, so that they are widely employed. Although the lithium-manganese composite oxides are low in their capacities and bad in their high temperature cyclic characteristics, they are more excellent than the lithium-cobalt composite oxides in view of costs and stability in supply of raw materials, and accordingly, they have been greatly anticipated and the study of them has been advanced.
As the configurations of the lithium-ion secondary batteries, there may be exemplified a cylindrical battery in which a spirally coiled electrode element is inserted into a cylindrical case and a rectangular battery in which a folded electrode or a rectangular laminated electrode element or a coiled electrode element formed by winding long bond shape cathodes and anodes is inserted into a rectangular case. The rectangular battery as the latter is higher in its space efficiency than that of the cylindrical battery. Thus, a demand for the rectangular battery has been recently increased, since the thickness of the portable electronic devices has been lately decreased.
Since the above described compact secondary battery is used not only in an ordinary state, but also in a vehicle in the mid-summer day, high reliability is required for the secondary battery. Particularly, since the strength of a rectangular battery can is lower than that of a cylindrical battery can, it is apt to be deformed due to the increase of internal pressure of the battery. Therefore, in using case of a rectangular battery which is accommodated in the electronic device, when the battery is exposed to high temperature, the battery may possibly expand due to the decomposition of the electrolyte solution in the battery, which will cause the breakage of the battery or the damage of the device.
However, in the information terminal of a note book type personal computer on which a high performance CPU is mounted, the rise of temperature due to the heat generated from the CPU recently gives an adverse influence to the battery. Therefore, although a fan for releasing the heat is installed in the vicinity of the CPU, it cannot be said that only this countermeasure completely prevents the adverse influence. Further, since it is expected that a higher performance CPU is adopted in the future, a worse influence may be possibly applied to the battery. In the nonaqueous secondary battery using the lithium-manganese composite oxides, the characteristic thereof is similar to that of the lithium-cobalt composite oxides or the lithium-nickel composite oxides at ambient temperature, however, a cyclic characteristic is incomplete at high temperature, because an insufficient battery property is obtained at high temperature (45° C. to 60° C.) resulting from a spinel lithium-manganese oxide. Especially, since the CPU operates and charging and discharging cycles are frequently repeated at about 45° C. in the note book type personal computer, the lithium-manganese composite oxides cannot be used, unless the battery properties at the high temperature (45° C. to 60° C.) resulting from the spinel lithium-manganese oxide are improved. Further, since the above described secondary battery is employed not only for the note book type personal computer, but also for other portable electronic devices, the cyclic characteristics at low temperature and ambient temperature are equally important.